Disease‐specific phenotypes in dopamine neurons from human iPS‐based models of genetic and sporadic Parkinson's disease

Abstract

Induced pluripotent stem cells (iPSC) offer an unprecedented opportunity to model human disease in relevant cell types, but it is unclear whether they could successfully model age-related diseases such as Parkinson's disease (PD). Here, we generated iPSC lines from seven patients with idiopathic PD (ID-PD), four patients with familial PD associated to the G2019S mutation in the Leucine-Rich Repeat Kinase 2 (LRRK2) gene (LRRK2-PD) and four age- and sex-matched healthy individuals (Ctrl). Over long-time culture, dopaminergic neurons (DAn) differentiated from either ID-PD- or LRRK2-PD-iPSC showed morphological alterations, including reduced numbers of neurites and neurite arborization, as well as accumulation of autophagic vacuoles, which were not evident in DAn differentiated from Ctrl-iPSC. Further induction of autophagy and/or inhibition of lysosomal proteolysis greatly exacerbated the DAn morphological alterations, indicating autophagic compromise in DAn from ID-PD- and LRRK2-PD-iPSC, which we demonstrate occurs at the level of autophagosome clearance. Our study provides an iPSC-based in vitro model that captures the patients' genetic complexity and allows investigation of the pathogenesis of both sporadic and familial PD cases in a disease-relevant cell type.

Cellular processes associated with LRRK2 function and dysfunction

“…The use of human fibroblasts carrying LRRK2 pathogenic mutations has confirmed an alteration in autophagy with reports suggesting an increase in basal macroautophagy in G2019S carriers 113, or an impaired response to starvation‐induced macroautophagy across mutations in the LRRK2 catalytic core ( G2019S , Y1699C and R1441G ) 114. The use of induced Pluripotent Stem cell (iPSC)‐derived, human dopaminergic neurons carrying G2019S ‐LRRK2 has confirmed a reduction in macroautophagy in comparison with healthy controls 115; but again, details of the molecular mechanism underlying this are still ambiguous. The recent identification of potential interactors of LRRK2 such as Rab7L1, GAK, BAG5, Rab32 and endophilin A (EndoA) 116, 117, 118, and the description of an autophagy/lysosomal phenotype that can be corrected by Rab9 in mutant Drosophila 119 suggest that the study of LRRK2 in autophagy should probably be considered with a much wider prospective, taking into account a possible involvement of LRRK2 in vesicles dynamics in general.…”

The role of protein clearance mechanisms in organismal ageing and age-related diseases

“…Furthermore, both ESCs exhibit higher autophagy activity on early differentiation 71 . In addition, induced pluripotent stem cells generated from patients with PD show more autophagic vacuoles when differentiated into dopaminergic neurons 72 suggesting an active rejuvenation step to generate a pool of 'healthy' cells. Taken together, these results raise an intriguing hypothesis: increased proteolytic systems maintain immortality of ESCs but they are further enhanced during the initial steps of differentiation to scavenge damaged proteins that could affect the function and senescence of the new cell lineage and, therefore, organismal ageing.…”

Glucocerebrosidase mutations and the pathogenesis of Parkinson disease

“…However, these clones, colonies derived from the same human donor, still exhibit large variability (Devine et al, 2011). This can lead to considerable phenotypic variability that is unrelated to their genotype and a differing efficiency to which iPSC lines differentiate into neurons (Sánchez-Danés et al, 2012). Genome editing has become a necessary step to introduce point mutations into the genome, resulting in clonal cell lines that are isogenic (Soldner et al, 2011).…”